This invention relates to a semiconductor light emitting device having a light emitting layer formed on an insulating substrate such as a sapphire substrate. More particularly, the invention relates to a semiconductor light emitting device adapted to prevent a semiconductor crystalline structure from being damaged by static electricity electrified on an insulator substrate, thereby improving reliability.
The light emitting chip (hereinafter referred to as "LED chip") 20 for emitting, for example, bluish light is generally structured by layers of a gallium nitride (GaN) based compound semiconductor on a sapphire substrate 21, as shown in FIG. 4. In such a structure, it is impossible to provide one electrode at a backside of the substrate 21. Consequently, an n-side electrode 29 is provided in electrical connection with an n-type layer at a portion exposed by partly etching the overlying semiconductor layers. Meanwhile, a p-side electrode 28 is provided in electrical connection with a p-side layer on a surface side of the semiconductor layers. This LED chip 20 is, for example, die-bonded in a recess formed at a tip of a first lead 11, as shown in FIG. 4. Wire bonding is made using gold wires between the p-side electrode 28 and a projection 11a formed at the tip of the first lead 11, and between the n-side electrode 29 and a tip of a second lead 12. These elements are encapsulated by a resin which is transparent for a light emitted by a light emitting layer of the chip to form a resin package 14, thus forming a light emitting lamp.
The bluish light LED chip 20, as stated above, uses an electrically insulating substrate as the substrate 21. The substrate 21 at a top surface is provided with a gallium nitride based compound semiconductor layer that is electrically connected to the n-side electrode 29. On the other hand, the substrate 21 at a backside surface is die-bonded through a non-conductive resin, and the chip is die-bonded in an electrically float state. In this state, if static electricity occurs, carriers (electrons or holes) are electrified and built up on the substrate 21. As a result, where a charge amount increases, the carriers move to the semiconductor layer, resulting in a problem that the carriers cause cracks in the semiconductor crystal structure and deteriorate light emitting characteristics.
The n-side electrode 29 may be connected to the first lead with the p-side electrode 28 connected to the second lead. Because the substrate 21 is electrically insulative as stated before, the die bonding for the LED chip 20 is usually by a non-conductive adhesive. The respective surfaces of the substrate 21 are electrically isolated, and the substrate if electrified with carriers has a potential difference.
As in the above-stated bluish-light semiconductor light emitting device, where an electrically-insulative material such as a sapphire is used for the substrate and the substrate at the respective surfaces are out of electrical connection, if static electricity occurs, the substrate has a potential difference between the respective surfaces. If the amount of charge increases to increase the potential difference, the carriers flow into the semiconductor layer, giving rise to a problem that cracks occur in the crystal structure and the light emitting characteristic is badly affected.